The changing rotational excitation of C3 in comet 9P/Tempel 1 during Deep Impact     

Máté Ádámkovics  Imke de Pater  Hy Spinrad 《Astrophysics and Space Science》2012,342(2):309-315

The 4050 Å band of C₃ was observed with Keck/HIRES echelle spectrometer during the Deep Impact encounter. We perform a 2-dimensional analysis of the exposures in order to study the spatial, spectral, and temporal changes in the emission spectrum of C₃. The rotational population distribution changes after impact, beginning with an excitation temperature of ～45 K at impact and increasing for 2 hr up to a maximum of 61±5 K. From 2 to 4 hours after impact, the excitation temperature decreases to the pre-impact value. We measured the quiescent production rate of C₃ before the encounter to be 1.0×10²³ s^?1, while 2 hours after impact we recorded a peak production rate of 1.7×10²³ s^?1. Whereas the excitation temperature returned to the pre-impact value during the observations, the production rate remained elevated, decreasing slowly, until the end of the 4 hr observations. These results are interpreted in terms of changing gas densities in the coma and short-term changes in the primary chemical production mechanism for C₃.  相似文献   

Theoretical investigation of interstellar C–C–O and C–O–C bonding backbone molecules     

Emmanuel E. Etim  Prasanta Gorai  Ankan Das  Elangannan Arunan 《Astrophysics and Space Science》2018,363(1):6

There are numerous complex organic molecules containing carbon and oxygen atoms which show either C–C–O or C–O–C bonding backbone. This paper examines altogether 51 C–C–O and C–O–C bonding backbone molecules from ten different isomeric groups (C₂H₂O, C₃H₂O, C₂H₄O, C₂H₄O₂, C₃H₄O, C₂H₆O, C₂H₆O₂, C₃H₆O, C₃H₆O₂, C₃H₈O) to summarize the present astronomical status of these molecules. Accurate calculations of enthalpy of formation of these molecules show that the isomers with C–C–O backbone are more stable than the C–O–C backbone. Interestingly, a detailed analysis of relevant astromolecules indicates that most of the observed astromolecules have the C–C–O backbone. As a matter of fact, of all the molecules examined in this study, 80% of the astronomically observed species have the C–C–O backbone while only 20% have the C–O–C backbone. In general, interstellar abundance of a molecule is controlled by some factors such as kinetics, formation and destruction pathways,thermodynamics etc. A proper consideration of these factors could explain the observed abundances of these molecules. All these possible key factors are discussed in this paper.  相似文献   

The Gas Production Rate and Coma Structure of Comet C/1995 O1 (Hale–Bopp)     

Morgenthaler  Jeffrey P.  Harris  Walter M.  Roesler  Frederick L.  Scherb  Frank  Anderson  Christopher M.  Doane  Nathaniel E.  Oliversen  Ronald J. 《Earth, Moon, and Planets》2002,90(1-4):77-87

The University of Wisconsin–Madison and NASA–Goddard conducted acomprehensive multi-wavelength observing campaign of coma emissionsfrom comet Hale–Bopp, including OH 3080 Å, [O I] 6300 Å H₂O⁺ 6158 Å, H Balmer-α 6563 Å, NH₂ 6330 Å, [C I] 9850 ÅCN 3879 Å, C₂ 5141 Å, C₃ 4062 Å,C I 1657 Å, and the UV and optical continua. In thiswork, we concentrate on the results of the H₂O daughter studies.Our wide-field OH 3080 Å measured flux agrees with other, similarobservations and the expected value calculated from published waterproduction rates using standard H₂O and OH photochemistry.However, the total [O I] 6300 Å flux determined spectroscopically overa similar field-of-view was a factor of 3-4 higher than expected.Narrow-band [O I] images show this excess came from beyond theH₂O scale length, suggesting either a previously unknown source of[O I] or an error in the standard OH + ν→ O(¹ D) + H branching ratio. The Hale–Bopp OH and[O I] distributions, both of which were imaged tocometocentric distances >1 × 10⁶ km, were more spatiallyextended than those of comet Halley (after correcting for brightnessdifferences), suggesting a higher bulk outflow velocity. Evidence ofthe driving mechanism for this outflow is found in the Hα lineprofile, which was narrower than in comet Halley (though likelybecause of opacity effects, not as narrow as predicted by Monte-Carlomodels). This is consistent with greater collisional coupling betweenthe suprathermal H photodissociation products and Hale–Bopp's densecoma. Presumably because of mass loading of the solar wind by ionsand ions by the neutrals, the measured acceleration of H₂O⁺ downthe ion tail was much smaller than in comet Halley. Tailwardextensions in the azimuthal distributions of OH 3080 Å,[O I], and [C I] , as well as a Doppler asymmetry in the[O I] line profile, suggest ion-neutral coupling. While thetailward extension in the OH can be explained by increased neutralacceleration, the [O I] 6300 Å and [C I] 9850 Å emissions show 13%and >200% excesses in this direction (respectively), suggesting anon-negligible contribution from dissociative recombination of CO⁺and/or electron collisional excitation. Thus, models including theeffects of photo- and collisional chemistry are necessary for the fullinterpretation of these data.  相似文献   

Polarimetry and Photometry of Comet C/2004 Q2 (Machholz)     

Sergey Velichko  Nikolai Kiselev  Feodor Velichko 《Earth, Moon, and Planets》2005,97(3-4):379-386

We present results of polarimetry and photometry of comet C/2004 Q2 (Machholz) obtained with the 0.7-m telescope of Institute of Astronomy at the Karazin Kharkiv National University on February 3 and 4, and March 4 and 14, 2005. The observations were carried out with a one-channel photoelectric photometer-polarimeter. The IHW continuum UC (λ3650/80 Å), BC (λ4845/65 Å), RC (λ6840/90 Å) and emission filters CN (λ3871/50 Å), C₃ (λ4060/70 Å), and C2 (λ5140/90 Å) were used. Degree of the comet polarization at phase angles ≈ 52° and ≈44° in the red continuum was close to that for so called dusty comets. The comet had a typical spectral gradient of polarization ΔP/Δλ=0.86% per 1000 Å. In the framework of the Haser model we have found the gas production rates Q of the CN, C₃ and C₂ species and the dust production rates Afρ on February 4 and March 14, 2005. The ratio log[Afρ (BC)/Q(CN)] was compared with data for other comets. The normalized spectral gradient of cometary dust S’(BC,RC) was 8.7%/1000 Å for February 4 and 17.0%/1000 Å for March 14. We conclude that comet C/2004 Q2 (Machholz) in many respects is a typical dusty comet.  相似文献   

Identification of C4H5, C4H4, C3H3 and CH3 radicals produced from the reaction of atomic carbon with propene: Implications for the atmospheres of Titan and giant planets and for the interstellar medium     

Chih-Hao Chin  Wei-Kan Chen  Wen-Jian Huang  Yi-Cheng Lin  Shih-Huang Lee 《Icarus》2013,222(1):254-262

We observed the products C₄H₅, C₄H₄, C₃H₃ and CH₃ of the C(³P) + C₃H₆ reaction using product time-of-flight spectroscopy and selective photoionization. The identified species arise from the product channels C₄H₅ + H, C₄H₄ + 2H and C₃H₃ + CH₃. Product isomers were identified via measurements of photoionization spectra and calculations of adiabatic ionization energy. Product C₄H₅ probably involves three isomers HCCCHCH₃, H₂CCCCH₃ and H₂CCCHCH₂. In contrast, products C₄H₄ and C₃H₃ involve exclusively HCCCHCH₂ and H₂CCCH, respectively. Reaction mechanisms are unraveled with crossed-beam experiments and quantum-chemical calculations. The ³P carbon atom attacks the π orbital of propene (C₃H₆) to form a cyclic complex c-H₂C(C)CHCH₃ that rapidly opens the ring to form H₂CCCHCH₃ followed by decomposition to HCCCHCH₃/H₂CCCCH₃/H₂CCCHCH₂ + H and H₂CCCH + CH₃; the corresponding branching ratios are 7:5:10:78 predicted with RRKM calculations at collision energy 4 kcal mol^?1. Nascent C₄H₅ with enough internal energy further decomposes to HCCCHCH₂ + H. Ratios of products C₄H₅, C₄H₄ and C₃H₃ are experimentally evaluated to be 17:8:75. This work provides a comprehensive look at product channels of the title reaction and gives implications for the formation of hydrocarbons in extra-terrestrial environments such as Titan and carbon-rich interstellar media. We suggest that the title reaction, hitherto excluded in any chemical networks, needs to be taken into account at least in the atmosphere of Titan and carbon-rich molecular clouds where rapid neutral–neutral reactions are dominant and carbon atoms and propene are abundant.  相似文献   

New Molecular Species in Comet C/1995 O1 (Hale-Bopp) Observed with the Caltech Ssubmillimeter Observatory     

Lis  D. C.  Mehringer  D. M.  Benford  D.  Gardner  M.  Phillips  T. G.  Bockelée-Morvan  D.  Biver  N.  Colom  P.  Crovisier  J.  Despois  D.  Rauer  H. 《Earth, Moon, and Planets》1997,78(1-3):13-20

We present millimeter-wave observations of HNCO, HC₃N, SO, NH₂CHO, H¹³CN, and H₃O⁺ in comet C/1995 O1 (Hale-Bopp)obtained in February–April, 1997 with the Caltech Submillimeter Observatory (CSO). HNCO, first detected at the CSO in comet C/1996B2 (Hyakutake), is securely confirmed in comet Hale-Bopp via observations of three rotational transitions. The derived abundance with respect to H₂O is (4-13) × 10^-4. HC₃N, SO, and NH₂CHO are detected for the first time in a comet. The fractional abundance of HC₃N based on observations of three rotational lines is (1.9 ± 0.2) × 10^-4. Four transitions of SO are detected and the derived fractional abundance, (2-8) ×10^-3, is higher than the upper limits derived from UV observations of previous comets. Observations of NH₂CHO imply a fractional abundance of (1-8) × 10^-4. H₃O is detected for the first time from the ground. The H¹³CN (3-2)transition is also detected and the derived HCN/H¹³CN abundance ratio is 90 ± 15, consistent with the terrestrial¹²C/¹³C ratio. In addition, a number of other molecular species are detected, including HNC, OCS, HCO⁺, CO⁺, and CN(the last two are first detections in a comet at radio wavelengths). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Models of the cometary coma in which abundances are calculated for various heliocentric distances     

Michael B. Swift  George F. Mitchell 《Icarus》1981,47(3):412-430

One-dimensional radial models of the chemistry in cometary comae have been constructed for heliocentric distances ranging from 2 to 0.125 AU. The coma's opacity to solar radiation is included and photolytic reaction rates are calculated. A parent volatile mixture similar to that found in interstellar molecular clouds is assumed. Profiles through the coma of number density and column density are presented for H₂O, OH, O, CN, C₂, C₃, CH, and NH₂. Whole-coma abundances are presented for NH₂, CH, C₂, C₃, CN, OH, CO⁺, H₂O⁺, CH⁺, N₂⁺, and CO₂⁺.  相似文献   

Spectra Of Split Comet C/1999 S4 (Linear)     

Churyumov  K. I.  Luk'yanyk  I. V.  Vlassyuk  V. V.  Borisov  N. V. 《Earth, Moon, and Planets》2002,90(1-4):141-146

We obtained spectra of comet C/1999 S4 (LINEAR) with the UAGS spectrograph(long slit and CCD) installed on the 1-m Zeiss reflector of the SAO of the RAS(Northern Caucuses, Nizhny Arkhyz) on July 23/24, 26/27 and 27/28, 2000. OnJuly 22/23, before the splitting of the cometary nucleus, several emission lines,such as C₂, C₃, CN, NH, CH, NH₂, CO⁺, H₂O⁺ wereclearly identified in the spectra. The inspections of the CCD spectra obtainedon July 27/28, 2000 reveals only very weak emission lines superimposed on thesolar reflection spectrum. From analyzing the surface brightness profile of C₂ along the slit the velocity of separation of two secondary fragments (V = 10 km/h) and the energy of the fragment separation (E = 8.7 × 10¹⁵ erg) were estimated. A luminescence cometary continuum of 26% of the total continuum level is detected in the spectra of the comet at 5000 Å. Possible mechanisms of nucleus splitting are discussed.  相似文献   

The organic composition of Comet C/2001 A2 (LINEAR): I. Evidence for an unusual organic chemistry     

Karen Magee-Sauer  Michael J. Mumma  Neil Dello Russo  Boncho P. Bonev  G.L. Villanueva 《Icarus》2008,194(1):347-356

We used the NIRSPEC instrument on the Keck-2 telescope atop Mauna Kea, HI to observe Comet C/2001 A2 (LINEAR) in a Target of Opportunity campaign on UT 2001 July 9.5, 10.5 August 4.4, 10.5. We measured seven organic parent volatiles (C₂H₆, C₂H₂, HCN, CH₄, CO, CH₃OH, H₂CO) simultaneously with H₂O. We obtained absolute production rates and relative abundances for parent volatiles, and also measured rotational temperatures for several of these species. The chemical composition of C/2001 A2 differs substantially from any comet we have observed to date. The abundances we measure (relative to H₂O) for C₂H₆, C₂H₂, HCN, and CH₃OH are enriched by a factor of ∼2 to 3 in C/2001 A2 compared with most comets in our database. Other molecular species were detected within the typical range of measured abundances. C/2001 A2 presented a unique opportunity to study the chemistry of a fragmenting comet where pristine areas are exposed to the Sun.  相似文献   

Products of meteoric metal ion chemistry within planetary atmospheres. 1. Mg at Titan     

Simon Petrie 《Icarus》2004,171(1):199-209

We report results of quantum chemical calculations of Mg⁺/ligand bond dissociation energies involving ligands identified as major constituents of Titan's upper atmosphere. Trends identified in these results allow elucidation of the important bimolecular and termolecular reactions of Mg⁺, and of simple molecular ions containing Mg⁺, arising from meteoric infall into Titan's atmosphere. Our study highlights, and includes calculated rate coefficients for, crucial ligand-switching and ligand-stripping reactions which ensure that a dynamic equilibrium exists between atomic and molecular ions of Mg⁺. Neutralization of ionized meteoric Mg is expected to produce the radical MgNC in high yield. The highly polar MgNC radical should provide an excellent nucleation site for condensation of polar (e.g., HCN, CH₃CN, and HC₃N) and highly unsaturated (e.g., C₂H₂, C₄H₂, and C₂N₂) neutrals at comparatively high altitude, leading to precipitation of Mg-doped tholin-like material. The implications for Titan's prebiotic chemical evolution, of the surface deposition of such material (which may feasibly contain magnesium porphyrins, or other bioactive Mg-containing complexes) remain to be assessed.  相似文献   

A Multi-Wavelength Simultaneous Study of the Composition of the Halley Family Comet 8P/Tuttle     

E. Jehin  D. Bockelée-Morvan  N. Dello Russo  J. Manfroid  D. Hutsemékers  H. Kawakita  H. Kobayashi  R. Schulz  A. Smette  J. Stüwe  M. Weiler  C. Arpigny  N. Biver  A. Cochran  J. Crovisier  P. Magain  H. Rauer  H. Sana  R. J. Vervack  H. Weaver  J.-M. Zucconi 《Earth, Moon, and Planets》2009,105(2-4):343-349

We report on simultaneous optical and infrared observations of the Halley Family comet 8P/Tuttle performed with the ESO Very Large Telescope. Such multi-wavelength and coordinated observations are a good example of what can be done to support space missions. From high resolution optical spectroscopy of the CN (0,0) 388 nm and NH₂ (0,9,0) 610 nm bands using UVES at UT2 we determined ¹²C/¹³C = 90 ± 10 and ¹⁴N/¹⁵N = 150 ± 20 in CN and we derived a nuclear spin temperature of NH₃ of 29 ± 1 K. These values are similar to those found in Oort-Cloud and Jupiter Family comets. From low resolution long slit spectroscopy with FORS1 at UT2 we determined the CN, C₃ and C₂ production rates and the parent and daughter scale lengths up to 5.2 10⁵ km tailward. From high resolution IR spectroscopy with CRIRES at UT1 we measured simultaneously the production rates and mixing ratios of H₂O, HCN, C₂H₂, CH₄, C₂H₆, and CH₃OH.  相似文献   

On the photochemical formation of CN,C2, and C3 radicals in cometary comae     

Tetsuo Yamamoto 《Earth, Moon, and Planets》1981,24(4):453-463

The formation of cometary CN, C₂ and C₃ radicals is investigated in a photochemical reaction scheme. From an analysis of the observed brightness profiles of these radicals, it is shown that CN is formed as a primary product in the photolysis of its parent molecules, whereas C₂ and C₃ are formed via two-step photodissociation of their parents. We suggest that major parent of C₂ is different species from those of CN and C₃ on the basis of the difference of the variation with heliocentric distance of the sublimation rate of the parents of these radicals. Parent molecules and reaction schemes for the formation of these radicals are discussed.  相似文献   

Radial distribution of production rates, loss rates and densities corresponding to ion masses ?40 amu in the inner coma of Comet Halley: Composition and chemistry     

S.A. Haider 《Icarus》2005,177(1):196-216

In this paper we have studied the chemistry of C, H, N, O, and S compounds corresponding to ions of masses ?40 amu in the inner coma of the Comet 1P/Halley. The production rates, loss rates, and ion mass densities are calculated using the Analytical Yield Spectrum approach and solving coupled continuity equation controlled by the steady state photochemical equilibrium condition. The primary ionization sources in the model are solar EUV photons, photoelectrons, and auroral electrons of the solar wind origin. The chemical model couples ion-neutral, electron-neutral, photon-neutral and electron-ion reactions among ions, neutrals, electrons, and photons through over 600 chemical reactions. Of the 46 ions considered in the model the chemistry of 24 important ions (viz., CH₃OH⁺₂, H₃CO⁺, NH⁺₄, H₃S⁺, H₂CN⁺, H₂O⁺, NH⁺₃, CO⁺, C₃H⁺₃, OH⁺, H₃O⁺, CH₃OH⁺, C₃H⁺₄, C₂H⁺₂, C₂H⁺, HCO⁺, S⁺, CH⁺₃, H₂S⁺, O⁺, C⁺, CH⁺₄, C⁺₂, and O⁺₂) are discussed in this paper. At radial distances <1000 km, the electron density is mainly controlled by 6 ions, viz., NH⁺₄, H₃O⁺, CH₃OH⁺₂, H₃S⁺, H₂CN⁺, and H₂O⁺, in the decreasing order of their relative contribution. However, at distances >1000 km, the 6 major ions are H₃O⁺, CH₃OH⁺₂, H₂O⁺, H₃CO⁺, C₂H⁺₂, and NH⁺₄; along with ions CO⁺, OH⁺, and HCO⁺, whose importance increases with further increase in the radial distance. It is found that at radial distances greater than ∼1000 km (±500 km) the major chemical processes that govern the production and loss of several of the important ions in the inner coma are different from those that dominate at distances below this value. The importance of photoelectron impact ionization, and the relative contributions of solar EUV, and auroral and photoelectron ionization sources in the inner coma are clearly revealed by the present study. The calculated ion mass densities are compared with the Giotto Ion Mass Spectrometer (IMS) and Neutral Mass Spectrometer (NMS) data at radial distances 1500, 3500, and 6000 km. There is a reasonable agreement between the model calculation and the Giotto measurements. The nine major peaks in the IMS spectra between masses 10 and 40 amu are reproduced fairly well by the model within a factor of two inside the ionopause. We have presented simple formulae for calculating densities of the nine major ions, which contribute to the nine major peaks in the IMS spectra, throughout the inner coma that will be useful in estimating their densities without running the complex chemical models.  相似文献   

Optical Spectroscopy of Comet C/2000 WM1 (LINEAR) at the Guillermo Harro Astrophysical Observatory in Mexico     

Churyumov  Klim I.  Luk'yanyk  Igor V.  Berezhnoi  Alexei A.  Chavushyan  Vahram H.  Sandoval  Lourdes S.  Palma  Alejandro A. 《Earth, Moon, and Planets》2002,90(1-4):361-368

We present a preliminary analysis of medium resolution optical spectra of comet C/2000 WM1 (LINEAR) obtained on 22 November 2001. Theemission lines of the molecules C₂, C₃, CN, NH₂,H₂O⁺ and presumably CO (Asundi and triplet bands) and C₂ ^-were identified in these spectra. By analysing the brightnessdistributions of the C₂, C₃, CN emission lines along theslit of the spectrograph we determined some physical parameters of theseneutrals, such as their lifetimes and expansion velocities inthe coma. The Franck–Condon factors for the CO Asundi bands and C₂ ^- bands were calculated using a Morse potential model.  相似文献   

Suggestion for searh of ethylene oxide ($$-C2H4O) in a osmi objet     

M. K. Sharma  M. Sharma  S. Chandra 《Astrophysics and Space Science》2018,363(5):94

Ethylene oxide (\(c\)-C₂H₄O) and its isomer acetaldehyde (CH₃CHO) are important organic molecules because of their potential role in the formation of amino acids. The \(c\)-C₂H₄O molecule is a \(b\)-type asymmetric top molecule and owing to half-spin of each of the four hydrogen atoms, it has two distinct ortho (nuclear spin one) and para (nuclear spin zero and two) species. It has been detected in the Sgr B2N. Using the rotational and centrifugal distortion constants along with the electric dipole moment, we have calculated energies of 100 rotational levels of each of the ortho and para species of \(c\)-C₂H₄O molecule and the Einstein \(A\)-coefficients for radiative transitions between the levels. The values of Einstein \(A\)-coefficients along with the scaled values for the collisional rate coefficients are used for solving a set of statistical equilibrium equations coupled with the equations of radiative transfer.Brightness-temperatures of five rotational transitions of each of the ortho and para species of \(c\)-C₂H₄O molecule are investigated. Out of these ten transitions, three transitions are found to show the anomalous absorption and rest seven are found to show the emission feature. We have also investigated seven transitions observed unblended in the Sgr B2(N). We have found that the transitions \(3_{3 0} - 3_{2 1}\) (23.134 GHz), \(2_{2 0} - 2_{1 1}\) (15.603 GHz), \(3_{3 1} - 3_{2 2}\) (39.680 GHz) and \(1_{1 1} - 0_{0 0}\) (39.582 GHz) may play important role for the identification of ethylene oxide in a cosmic object.  相似文献   

Infrared measurements of the chemical composition of C/2006 P1 McNaught     

Neil Dello Russo  Ronald J. Vervack Jr.  Harold A. Weaver  Carey M. Lisse 《Icarus》2009,200(1):271-279

C/2006 P1 McNaught is a dynamically new comet from the Oort cloud that passed very close to the Sun, driving overall volatile production rates up to about 10³¹ molecules s⁻¹. Post-perihelion observations were obtained in a target-of-opportunity campaign using the CSHELL instrument at the NASA Infrared Telescope Facility atop Mauna Kea, Hawaii, on UT 2007 January 27 and 28. Eight parent volatiles (H₂O, CH₄, C₂H₂, C₂H₆, HCN, CO, NH₃, H₂CO) and two daughter fragments (OH and NH₂) were detected, enabling the determination of a rotational temperature and production rate for H₂O on UT January 27 and absolute and relative production rates for all the detected parent species on UT January 28. The chemical composition measured in the coma suggests that this close perihelion passage stripped off processed outer surface layers, likely exposing relatively fresh primordial material during these observations. The post-perihelion abundances we measure for CO and CH₄ (relative to H₂O) are slightly depleted while C₂H₂, NH₂ and possibly NH₃ are enhanced when compared to the overall comet population. Measured abundances for other detected molecular species were within the range typically observed in comets.  相似文献   

The role of ion-molecule reactions in the conversion of N₂O₅ to HNO₃ in the stratosphere     

H. Böhringer  D.W. Fahey  F.C. Fehsenfeld  E.E. Ferguson 《Planetary and Space Science》1983,31(2):185-191

We have investigated the role of several ion-molecule reactions in the conversion of N₂O₅ to HNO₃. In the proposed conversion, an N₂O₅ molecule would react with an H₂O molecule clustered to an inert ion to produce two HNO₃ molecules. Subsequent clustering of an H₂O molecule to the inert ion would make the reaction catalytic. If such an ion-catalysed conversion of N₂O₅ to HNO₃ occurs, it would probably play a role in the stratospheric chemistry at high latitudes in winter. In this paper we present reaction rate constant measurements made in a flowing afterglow apparatus for hydrated H₃O⁺, H⁺(CH₃CN)_m (m = 1, 2, 3), and several negative ions reacting with N₂O₅. Slow rate constants were found for these ions for hydration levels that are predominant in the stratosphere. With the known stratospheric ion density, these slow rate constants preclude significant N₂O₅ conversion by ion-molecule reactions.  相似文献   

Shock waves and the chemical structure of interstellar clouds     

M. Y. Amin  M. S. El-Nawawy  M. A. El-Shalaby 《Astrophysics and Space Science》1991,185(2):277-294

In this paper we study the effect of shock waves on the chemical structure of the interstellar clouds. A model of molecular cloud has been assumed. The chemistry is investigated in a time dependent model. Our chemical network contains 56 species in 251 reactions to including molecules of the elements H, O, C, N, S, and Si.The results indicate that the calculated fractional abundance of the molecules NS, H₂O, CN, NH, CO, and SO agrees well with the observations. The molecules OH, H₂S, CS, H₂CS, HS, NO, SiO, CH, CH₂, CH₃, HCO, C₂, and HCN reach high post-shock abundances.  相似文献   

Energy transfer from excited N₂ and O₂ as a source of O(¹S) in the Aurora     

A.W. Yau  G.G. Shepherd 《Planetary and Space Science》1979,27(4):481-490

It is proposed that energy transfer from excited O₂ contributes to the production of O(¹S) in aurora. An analysis is presented of the OI5577 Å emission in an IBC II⁺ aurora between 90 and 130 km. The volume emission rate of the emission at these altitudes is consistent with the production rate of O(¹S) by energy transfer to O(³P) from N₂ in the A³Σ₂⁺ state and O₂ in the A³Σ_u⁺, C³Δc¹Σ_u^? states, the N₂A state being populated by direct electron impact excitation and B → A cascade and the excited O₂ states by direct excitation. Above the peak emission altitude (~105 km), energy transfer from N₂A is the predominant production mechanism for O(¹S). Below it, the contribution from quenching of the O₂ states becomes significant.  相似文献   

Mutual neutralization rates of ionospherically important ions     

D. Smith  N.G. Adams  M.J. Church 《Planetary and Space Science》1976,24(7):697-703

Following our recently published measurements of the rate coefficients for mutual neutralization, α, of the ionospherically important reactions NO⁺ + NO₂^?(α₁) and NO⁺ + NO₃^?(α₂) carried out in ion-ion flowing afterglow plasmas at 300 K, we have determined the mutual neutralization rates for the water cluster ion H₃O⁺ · (H₂O)₃ with a mixture of several negative ions which are known to exist in the D region. The α coefficients for these cluster ion reactions do not differ significantly from alpha;₁ and α₂, all of these reactions having α ?6 × 10^?8 cm³/sec which is significantly smaller than values usually adopted in ionospheric calculations. Current information on the ionic composition of the D region and the implications of the present results to de-ionization rate calculations are discussed.  相似文献